Meteorite-Impact Craters

Given that Antarctica has an area of 14.2 million square kilometers, it should contain about 16 meteorite impact craters like those that have been preserved on the other continents. 

Although large meteorites have certainly impacted in Antarctica, only one such crater has been tentatively identified under the ice at about 71°30 S, 140°00 E in Wilkes Land south of the Adelie coast. Another more speculative meteorite impact crater may exist at Butcher Ridge (79°12 S, 155°48 E) in the Cook Mountains of southern Victoria Land. 

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Defects in Crushed Si02 and Those of Quartz in Meteorite Impact Crater. 

Bloch, M. R., Fechtig, H., Gentner, W., Neukum, G., Schneider, E. (1971) Meteorite impact craters, crater simulations, and the meteoroid flux in the early solar system. Proc. Second Lunar Science Conf., 3, 2639-52. 

Q-Quartz, which has a trigonal crystal structure, undergoes a rapid, reversible transition to hexagonal /J-quartz at 573 °C and then slowly changes to hexagonal /3-tridymite at about 870 °C tridymite in turn goes over slowly to cubic /3-cristobalite at 1470 °C, and this melts at 1713 °C. The reversion of cristobalite and tridymite to quartz is slow, so that these forms can exist at room temperature (as a-modifications). In addition, dense modifications with six-coordinate Si are found in shocked rocks associated with meteorite impact craters coesite forms only above 450 °C and 3.8 GPa, and stishovite requires over 1200 °C and 13 GPa. Survival of those metastable polymorphs on the geological timescale is evidence of an extremely slow recrystallization rate. 

Apart from the Raman spectroscopic identification of two different types of bacteria in a gypsum crystal Nostoc and Gloeocapsa), it was also possible to detect organic signatures from bacterial colonies sited several millimetres below the surface in a transparent crystal of selenite from a 26 Mya meteoritic impact crater [37] at Devon Island in the Canadian High Arctic (Figure 1-9). 

Figure 1-9. (Selenite var. gypsum) deposits, Haughton meteorite impact crater, Devon Island, Canadian...

I. Martinez and P. Agrinier, Meteorite impact craters on Earth major shock-induced effects in rocks and minerals. C.R. Acad. Sci. Paris, Sciences de la terre et des planetes 327, pp. 75-86 (1998). 

The presence of a meteorite impact crater at 71.5°S and 140°E in Wilkes Land was first suggested by Schmidt (1962) as a potential source of tektites in Australia called australites based on the presence of a negative gravity anomaly that was recorded by the Victoria Land Traverse-2 in 1958/59. The presence of a meteorite impact crater in WUkes Land was supported by Weihaupt (1961,1976) on the basis of a seismic survey which indicated that the elevation of the bedrock surface at the site of the hypothetical crater is 415... 

Fig. 18.7 The Wilkes Land subgladal meteorite-impact crater was identified on the basis of gravity data obtained by the GRACE sateUite (Gravity Recovery and Climate Experiment). The location of the crater is indicated by a positive free-air gravity anomaly which occurs above a subglacial basin at 70°S and 120°E outlined by the solid white lines which delineate the rim of the crater. The dashed lines outline the hypothetical outer rings of this multi-ring basin. The coincidence of a positive gravity anomaly over a deep...

This alternative explanation is based on extensive information derived from the study of meteorite impact craters (e.g., Koeberl 1994 Dressier et al. 1994 Koeberl and MacLeod 2002). Unfortunately experts familiar with hypervelocity impacts of large meteorites have not had an opportunity to examine the rocks at Butcher Ridge. 

USA), and has since been identified in further meteorites, impact crater sites (such as Tunguska, Russia), in diamond placer deposits and high-grade metamorphic rocks (Golovnya et ah, 1977). It occurs as microscopic brown to brown-yellow or black crystals, usually as disseminated grains or as aggregates. Lonsdaleite is a rare mineral and unlikely to have been used as a pigment (Winter, 1983) it is included here, however, for completeness in the discussion of crystalline carbons. 

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